ig.module(
	'impact.entity'
)
.requires(
	'impact.animation',
	'impact.impact'
)
.defines(function(){

ig.Entity = ig.Class.extend({
	id: 0,
	settings: {},
	
	size: {x: 16, y:16},
	offset: {x: 0, y: 0},
	
	pos: {x: 0, y:0},
	last: {x: 0, y:0},
	vel: {x: 0, y: 0},
	accel: {x: 0, y: 0},
	friction: {x: 0, y: 0},
	maxVel: {x: 100, y: 100},
	zIndex: 0,
	gravityFactor: 1,
	standing: false,
	bounciness: 0,
	minBounceVelocity: 40,
	
	anims: {},
	animSheet: null,
	currentAnim: null,
	health: 10,
	
	type: 0, // TYPE.NONE
	checkAgainst: 0, // TYPE.NONE
	collides: 0, // COLLIDES.NEVER
	
	init: function( x, y, settings ) {
		this.id = ++ig.Entity._lastId;
		this.pos.x = x;
		this.pos.y = y;
		
		ig.merge( this, settings );
	},
	
	addAnim: function( name, frameTime, sequence, stop ) {
		if( !this.animSheet ) {
			throw( 'No animSheet to add the animation '+name+' to.' );
		}
		var a = new ig.Animation( this.animSheet, frameTime, sequence, stop );
		this.anims[name] = a;
		if( !this.currentAnim ) {
			this.currentAnim = a;
		}
		
		return a;
	},
	
	update: function() {
		this.last.x = this.pos.x;
		this.last.y = this.pos.y;
		this.vel.y += ig.game.gravity * ig.system.tick * this.gravityFactor;
		
		this.vel.x = this.getNewVelocity( this.vel.x, this.accel.x, this.friction.x, this.maxVel.x );
		this.vel.y = this.getNewVelocity( this.vel.y, this.accel.y, this.friction.y, this.maxVel.y );
		
		// movement & collision
		var mx = this.vel.x * ig.system.tick;
		var my = this.vel.y * ig.system.tick;
		var res = ig.game.collisionMap.trace( 
			this.pos.x, this.pos.y, mx, my, this.size.x, this.size.y
		);
		this.handleMovementTrace( res );
		
		if( this.currentAnim ) {
			this.currentAnim.update();
		}
	},
	
	
	getNewVelocity: function( vel, accel, friction, max ) {
		if( accel ) {
			return ( vel + accel * ig.system.tick ).limit( -max, max );
		}
		else if( friction ) {
			var delta = friction * ig.system.tick;
			
			if( vel - delta > 0) {
				return vel - delta;
			} 
			else if( vel + delta < 0 ) {
				return vel + delta;
			}
			else {
				return 0;
			}
		}
		return vel.limit( -max, max );
	},
	
	
	handleMovementTrace: function( res ) {
		this.standing = false;
		if( res.collision.y ) {
			if( this.bounciness > 0 && Math.abs(this.vel.y) > this.minBounceVelocity ) {
				this.vel.y *= -this.bounciness;				
			}
			else {
				if( this.vel.y > 0 ) {
					this.standing = true;
				}
				this.vel.y = 0;
			}
		}
		if( res.collision.x ) {
			if( this.bounciness > 0 && Math.abs(this.vel.x) > this.minBounceVelocity ) {
				this.vel.x *= -this.bounciness;				
			}
			else {
				this.vel.x = 0;
			}
		}
		this.pos = res.pos;
	},
	
	
	draw: function() {
		if( this.currentAnim ) {
			this.currentAnim.draw(
				this.pos.x.round() - this.offset.x - ig.game.screen.x,
				this.pos.y.round() - this.offset.y - ig.game.screen.y
			);
		}
	},
	
	
	kill: function() {
		ig.game.removeEntity( this );
	},
	
	
	receiveDamage: function( amount, from ) {
		this.health -= amount;
		if( this.health <= 0 ) {
			this.kill();
		}
	},
	
	
	touches: function( other ) {		
		return !(
			this.pos.x > other.pos.x + other.size.x ||
			this.pos.x + this.size.x < other.pos.x ||
	        this.pos.y > other.pos.y + other.size.y ||
			this.pos.y + this.size.y < other.pos.y
		);
	},
	
	
	distanceTo: function( other ) {
		var xd = (this.pos.x + this.size.x/2) - (other.pos.x + other.size.x/2); 
		var yd = (this.pos.y + this.size.y/2) - (other.pos.y + other.size.y/2);
		return Math.sqrt( xd*xd + yd*yd );
	},
	
	
	angleTo: function( other ) {
		return Math.atan2(
			(other.pos.y + other.size.y/2) - (this.pos.y + this.size.y/2),
			(other.pos.x + other.size.x/2) - (this.pos.x + this.size.x/2)
		);
	},
	
	
	check: function( other ) {},
	collideWith: function( other, axis ) {}
});


// Last used entity id; incremented with each spawned entity

ig.Entity._lastId = 0;


// Collision Types - Determine if and how entities collide with each other

// In ACTIVE vs. LITE or FIXED vs. ANY collisions, only the "weak" entity moves,
// while the other one stays fixed. In ACTIVE vs. ACTIVE and ACTIVE vs. PASSIVE
// collisions, both entities are moved. LITE or PASSIVE entities don't collide
// with other LITE or PASSIVE entities at all. The behaiviour for FIXED vs.
// FIXED collisions is undefined.

ig.Entity.COLLIDES = {
	NEVER: 0,
	LITE: 1,
	PASSIVE: 2,
	ACTIVE: 4,
	FIXED: 8
};


// Entity Types - used for checks

ig.Entity.TYPE = {
	NONE: 0,
	A: 1,
	B: 2,
	BOTH: 3
};



ig.Entity.checkPair = function( a, b ) {
	
	// Do these entities want checks?
	if( a.checkAgainst & b.type ) {
		a.check( b );
	}
	
	if( b.checkAgainst & a.type ) {
		b.check( a );
	}
	
	// If this pair allows collision, solve it! At least one entity must
	// collide ACTIVE or FIXED, while the other one must not collide NEVER.
	if(
		a.collides && b.collides &&
		a.collides + b.collides > ig.Entity.COLLIDES.ACTIVE
	) {
		ig.Entity.solveCollision( a, b );
	}
};


ig.Entity.solveCollision = function( a, b ) {
	
	// If one entity is FIXED, or the other entity is LITE, the weak
	// (FIXED/NON-LITE) entity won't move in collision response
	var weak = null;
	if(
		a.collides == ig.Entity.COLLIDES.LITE ||
		b.collides == ig.Entity.COLLIDES.FIXED
	) {
		weak = a;
	}
	else if(
		b.collides == ig.Entity.COLLIDES.LITE ||
		a.collides == ig.Entity.COLLIDES.FIXED
	) {
		weak = b;
	}
		
	
	// Did they already overlap on the X-axis in the last frame? If so,
	// this must be a vertical collision!
	if(
		a.last.x + a.size.x > b.last.x &&
		a.last.x < b.last.x + b.size.x
	) {
		// Which one is on top?
		if( a.last.y < b.last.y ) {
			ig.Entity.seperateOnYAxis( a, b, weak );
		}
		else {
			ig.Entity.seperateOnYAxis( b, a, weak );
		}
		a.collideWith( b, 'y' );
		b.collideWith( a, 'y' );
	}
	
	// Horizontal collision
	else if(
		a.last.y + a.size.y > b.last.y &&
		a.last.y < b.last.y + b.size.y
	){
		// Which one is on the left?
		if( a.last.x < b.last.x ) {
			ig.Entity.seperateOnXAxis( a, b, weak );
		}
		else {
			ig.Entity.seperateOnXAxis( b, a, weak );
		}
		a.collideWith( b, 'x' );
		b.collideWith( a, 'x' );
	}
};


// FIXME: This is a mess. Instead of doing all the movements here, the entities
// should get notified of the collision (with all details) and resolve it
// themselfs.

ig.Entity.seperateOnXAxis = function( left, right, weak ) {
	var nudge = (left.pos.x + left.size.x - right.pos.x);
	
	// We have a weak entity, so just move this one
	if( weak ) {
		var strong = left === weak ? right : left;
		weak.vel.x = -weak.vel.x * weak.bounciness + strong.vel.x;
		
		var resWeak = ig.game.collisionMap.trace( 
			weak.pos.x, weak.pos.y, weak == left ? -nudge : nudge, 0, weak.size.x, weak.size.y
		);
		weak.pos.x = resWeak.pos.x;
	}
	
	// Normal collision - both move
	else {
		var v2 = (left.vel.x - right.vel.x)/2;
		left.vel.x = -v2;
		right.vel.x = v2;
	
		var resLeft = ig.game.collisionMap.trace( 
			left.pos.x, left.pos.y, -nudge/2, 0, left.size.x, left.size.y
		);
		left.pos.x = resLeft.pos.x.floor();
		
		var resRight = ig.game.collisionMap.trace( 
			right.pos.x, right.pos.y, nudge/2, 0, right.size.x, right.size.y
		);
		right.pos.x = resRight.pos.x.ceil();
	}
};


ig.Entity.seperateOnYAxis = function( top, bottom, weak ) {
	var nudge = (top.pos.y + top.size.y - bottom.pos.y);
	
	// We have a weak entity, so just move this one
	if( weak ) {
		var strong = top === weak ? bottom : top;
		weak.vel.y = -weak.vel.y * weak.bounciness + strong.vel.y;
		
		// Riding on a platform?
		var nudgeX = 0;
		if( weak == top && Math.abs(weak.vel.y - strong.vel.y) < weak.minBounceVelocity ) {
			weak.standing = true;
			nudgeX = strong.vel.x * ig.system.tick;
		}
		
		var resWeak = ig.game.collisionMap.trace( 
			weak.pos.x, weak.pos.y, nudgeX, weak == top ? -nudge : nudge, weak.size.x, weak.size.y
		);
		weak.pos.y = resWeak.pos.y;
		weak.pos.x = resWeak.pos.x;
	}
	
	// Bottom entity is standing - just bounce the top one
	else if( ig.game.gravity && (bottom.standing || top.vel.y > 0) ) {	
		var resTop = ig.game.collisionMap.trace( 
			top.pos.x, top.pos.y, 0, -(top.pos.y + top.size.y - bottom.pos.y), top.size.x, top.size.y
		);
		top.pos.y = resTop.pos.y;
		
		if( top.bounciness > 0 && top.vel.y > top.minBounceVelocity ) {
			top.vel.y *= -top.bounciness;		
		}
		else {
			top.standing = true;
			top.vel.y = 0;
		}
	}
	
	// Normal collision - both move
	else {
		var v2 = (top.vel.y - bottom.vel.y)/2;
		top.vel.y = -v2;
		bottom.vel.y = v2;
		
		var nudgeX = bottom.vel.x * ig.system.tick;
		var resTop = ig.game.collisionMap.trace( 
			top.pos.x, top.pos.y, nudgeX, -nudge/2, top.size.x, top.size.y
		);
		top.pos.y = resTop.pos.y;
		
		var resBottom = ig.game.collisionMap.trace( 
			bottom.pos.x, bottom.pos.y, 0, nudge/2, bottom.size.x, bottom.size.y
		);
		bottom.pos.y = resBottom.pos.y;
	}
};

});